1. Technical Field
The present invention relates to an information processing device for identifying and processing characteristic information of a recording medium, to an access device equipped with this information processing device, to a recording medium accessed by this access device, and to an information processing method and information processing program thereof.
2. Background Art
Vast amounts of information are used in communications today. This has prompted the development of large-capacity optical disks. Optical disks include compact disks (CD), laser discs (LD), and digital versatile discs (DVD).
The reproduction of information with an optical disk is performed by forming a reflective film composed of a metal thin film (such as aluminum) on a transparent substrate in which a textured pattern (such as pits or grooves) that convey information has been formed, and detecting the level of reflection of light from this pattern.
Recordable optical disks are formed with a characteristic pattern whose reflectance changes with the phase change of the recording film. Because an optical disk device need only read the change in reflectance between amorphous and crystalline phases, the optical system of an optical disk device can have a simple structure.
An optical disk device reproduces information recorded on the basis of phase change by detecting the reflection levels of a plurality of recorded portions and a plurality of unrecorded portions. Therefore, an optical disk can either be one having a characteristic such that the reflectance of light reflected by the plurality of recorded portions is greater than the reflectance of light reflected by the plurality of unrecorded portions (L-to-H characteristic), or one having a characteristic such that the reflectance of light reflected by the plurality of recorded portions is less than the reflectance of light reflected by the plurality of unrecorded portions (H-to-L characteristic).
FIG. 7 shows the relation between the reflection level of light reflected by an optical disk and a plurality of recording marks formed on the optical disk. FIG. 7A shows the relation between the reflection level of light reflected by an optical disk having an H-to-L characteristic and a plurality of recording marks formed on an optical disk having an H-to-L characteristic. FIG. 7B shows the relation between the reflection level of light reflected by an optical disk having an L-to-H characteristic and a plurality of recording marks formed on an optical disk having an L-to-H characteristic.
Amorphous portions (recorded portions, such as recording marks) in which the reflectance of light is about 1% are formed on an optical disk having an H-to-L characteristic (H-to-L type optical disk). The reflectance of light is 15 to 25% in the crystalline portions (unrecorded portions, such as spaces) of an H-to-L type optical disk (see FIG. 7A). Amorphous portions (recorded portions, such as recording marks) in which the reflectance of light is 20 to 30% are formed on an optical disk having an L-to-H characteristic (L-to-H type optical disk). The reflectance of light is 3 to 10% in the crystalline portions (unrecorded portions, such as spaces) of an L-to-H type optical disk (see FIG. 7B).
With an H-to-L type optical disk, focusing and tracking are easier because of the high reflectance of the unrecorded portions, but because the average reflectance of light is higher, there is more noise than with an L-to-H type optical disk.
With an L-to-H type optical disk, the average reflectance of light is lower, so there is less noise than with an H-to-L type optical disk, but because the reflectance is lower in the unrecorded portions, focusing and tracking are more difficult.
Patent Document 1 discusses both an H-to-L type optical disk and an L-to-H type optical disk.
Patent Document 1: Japanese Laid-Open Patent Application 2003-323744